Process for making rigid and flexible polyurethane foams containing a fire-retardant

ABSTRACT

Process for preparing rigid and flexible polyurethane foams by reacting a polyisocyanate, polyols and water in the presence of a catalyst and a fire retardant which is a combination of expandable graphite and phosphorous-containing compound.

“This application is a continuation of international application numberPCT EP00/08617, filed Sep. 4, 2000, (status, abandoned, pending, etc.).”

The present invention is concerned with the use of a fire retardant inpreparing rigid foams and flexible foams and with compositionscomprising such fire retardant.

The use of fire retardants in preparing polyurethane foams has beenwidely described. J02153967 discloses a polyurethane foam containingexpandable graphite and a fire-retardant agent such astris(2-chloroethyl)phosphate. EP-A-192888 discloses a polyurethane foamcontaining a fire-retardant agent comprising expandable graphite andoptionally other compounds such as phosphorous compounds. J51009197discloses a polyurethane foam containing a fire-retardant agentcomprising e.g. tricresylphosphate, where the foam further comprisescarbonaceous fibers.

Further conventional flexible polyurethane foams are widely known. Suchfoams show a relatively high resilience (ball rebound), a relatively lowmodulus, a relatively high sag factor and a relatively low hysteresisloss. Such foams further show a major glass-rubber transition belowambient temperature, generally in the temperature range of −100° C. to−10° C. The commonly applied relatively high molecular weight polyetherand polyester polyols in such foams are responsible for the sub-ambientglass transition temperature (Tg^(s)). These polyether and polyesterpolyols are often referred to as soft segments. Above Tg^(s) the foamdisplays its typical flexible properties until softening and/or meltingof the isocyanate-derived urethane/urea clusters (“hard domains”) takesplace. This softening and/or melting temperature (Tg^(h) and/or Tm^(h))often coincides with the onset of thermal degradation of polymersegments. The Tg^(h) and/or Tm^(h) for flexible polyurethane foams isgenerally higher than 100° C., often even exceeding 200° C. At theTg^(s) a sharp decrease of the modulus of the flexible foam is observed.Between Tg^(s) and Tg^(h)/Tm^(h) the modulus remains fairly constantwith increasing temperature and at Tg^(h)/Tm^(h) again a substantialdecrease of the modulus may take place. A way of expressing the presenceof Tg^(s) is to determine the ratio of the Young's storage modulus E′ at−100° C. and +25° C. as per Dynamic Mechanical Thermal Analysis (DMTAmeasured according to ISO/DIS 6721-5). For conventional flexiblepolyurethane foams the$\frac{E^{\prime}{­100{^\circ}}\quad {C.}}{E^{\prime} + {25{^\circ}\quad {C.}}}\quad {ratio}\quad {is}\quad {at}\quad {least}\quad 25.$

Another feature of Tg^(s) by DMTA (ISO/DIS 6721-5) is that forconventional flexible polyurethane foams the maximum value of the ratioof$\quad {\frac{{{Young}'}s\quad {loss}\quad {modulus}\quad E^{''}}{{{Young}'}s\quad {storage}\quad {modulus}\quad E^{\prime}}\left( \tan_{\delta \quad {\max.}} \right)}\quad$

over the −100° C./+25° C. temperature range varies from 0.20-0.80 ingeneral. The Young's loss modulus E″ is measured by DMTA (ISO/DIS6721-5) as well.

In patent application PCT/EP9601594 a completely new class of flexiblepolyurethane foams is described such foams having no major glass-rubbertransition between −100° C. and +25° C. In more quantitative terms thesefoams show a ratio

E′_(−100° C.)/E′_(+25° C.) of 1.3 to 15.0, preferably of 1.5 to 10 andmost preferably of 1.5 to 7.5. The tan _(δmax) over the −100° C. to +25°C. temperature range is below 0.2.

The apparent core density of such foams may range from 4-30 kg/m³ andpreferably ranges from 4-20 kg/m³ (measured according to ISO/DIS845).Such foams are made by crushing a rigid foam.

PCT/EP9806888 discloses a process substantially according to the one ofPCT/EP9601594, carried out in the presence of a fire retardant whereinthe fire retardant is selected from 1) polybrominated diphenyl ethers;2) dialkyl esters of polybrominated phthalic acid; 3) compounds offormula P(O)XYZ, wherein X, Y and Z are independently selected from thegroups —R and —OR wherein R is an aryl or aralkyl group having 6-12 andpreferably 6-10 carbon atoms; 4) mixtures of the compounds 1, 2 and 3and 5) mixtures of another fire retardant with any of the compounds 1, 2and 3 or with mixtures of the compounds 1, 2 and 3.

In the context of the present application hereinafter a flexiblepolyurethane foam is a crushed foam having a ball rebound (measuredaccording to ISO 8307) of at least 40%, preferably at least 50% and mostpreferably 55-85% in at least one of the three dimensional directionsand a sag factor (CLD 65/25) of at least 2.0 (measured according to ISO3386/1). Preferably such flexible foams have a Young's storage modulusat 25° C. of at most 500 kPa, more preferably at most 350 kPa and mostpreferably between 10 and 200 kPa (Young's storage modulus measured byDMTA according to ISO/DIS 6721-5). Further, such flexible foamspreferably have a sag factor (CLD 65/25) of at least 3.5 and mostpreferably 4.5-10 (measured according to ISO 3386/1). Still further suchflexible foams preferably have a CLD hysteresis loss (ISO 3386/1) ofbelow 55%, more preferably below 50% and most preferably below 45%.

In the context of the present patent application hereinafter a rigidpolyurethane foam is an uncrushed foam having a ball rebound measured inthe direction of foam rise of less than 40% (ISO 8307 with the provisothat no preflex conditioning is applied, that only one rebound value persample is measured and that test pieces are conditioned at 23° C.±2° C.and 50±5% relative humidity) and/or having a CLD 65/25 sag factormeasured in the direction of foam rise of less than 2.0 (ISO 3386/1 withthe proviso that the sag factor is determined after the firstload—unload cycle); these properties both being measured at a coredensity of the foam of 3-27 kg/m³ (ISO 845). Preferably the ratioE′_(−100° C.)/E′_(+25° C .)of such a rigid foam is 1.3-15. If in thepresent application ISO 8307 and ISO 3386/1 are mentioned in relation torigid foams they refer to the tests as described above including theprovisos.

In the context of the present invention the following terms have thefollowing meaning:

1) isocyanate index or NCO index or index:

the ratio of NCO-groups over isocyanate-reactive hydrogen atoms presentin a formulation, given as a percentage:$\frac{\lbrack{NCO}\rbrack \times 100}{\left\lbrack {{active}\quad {hydrogen}} \right\rbrack}{(\%).}$

In other words the NCO-index expresses the percentage of isocyanateactually used in a formulation with respect to the amount of isocyanatetheoretically required for reacting with the amount ofisocyanate-reactive hydrogen used in a formulation.

It should be observed that the isocyanate index as used herein isconsidered from the point of view of the actual foaming processinvolving the isocyanate ingredient and the isocyanate-reactiveingredients. Any isocyanate groups consumed in a preliminary step toproduce modified polyisocyanates (including such isocyanate-derivativesreferred to in the art as quasi or semi-prepolymers and prepolymers) orany active hydrogens consumed in a preliminary step (e.g. reacted withisocyanate to produce modified polyols or polyamines) are not taken intoaccount in the calculation of the isocyanate index. Only the freeisocyanate groups and the free isocyanate-reactive hydrogens (includingthose of the water) present at the actual foaming stage are taken intoaccount.

2) The expression “isocyanate-reactive hydrogen atoms” as used hereinfor the purpose of calculating the isocyanate index refers to the totalof active hydrogen atoms in hydroxyl and amine groups present in thereactive compositions; this means that for the purpose of calculatingthe isocyanate index at the actual foaming process one hydroxyl group isconsidered to comprise one reactive hydrogen, one primary amine group isconsidered to comprise one reactive hydrogen and one water molecule isconsidered to comprise two active hydrogens.

3) Reaction system: a combination of components wherein thepolyisocyanates are kept in one or more containers separate from theisocyanate-reactive components.

4) The expression “polyurethane foam” as used herein refers to cellularproducts as obtained by reacting polyisocyanates withisocyanate-reactive hydrogen containing compounds, using foaming agents,and in particular includes cellular products obtained with water asreactive foaming agent (involving a reaction of water with isocyanategroups yielding urea linkages and carbon dioxide and producingpolyurea-urethane foams) and with polyols, aminoalcohols and/orpolyamines as isocyanate-reactive compounds.

5) The term “average nominal hydroxyl functionality” is used herein toindicate the number average functionality (number of hydroxyl groups permolecule) of the polyol or polyol composition on the assumption thatthis is the number average functionality (number of active hydrogenatoms per molecule) of the initiator(s) used in their preparationalthough in practice it will often be somewhat less because of someterminal unsaturation.

6) The word “average” refers to number average unless indicatedotherwise.

7) pK_(a) refers to the strength of a protolyte compared to that ofwater (pK_(a)=−logK_(a) wherein K_(a) is the dissociation constant ofthe acid or the salt).

The foams according to the present invention are prepared by reacting apolyisocyanate (1), an isocyanate-reactive compound (2), said compound(2) having an average equivalent weight of at most 374 and an averagenumber of isocyanate-reactive hydrogen atoms of from 2 to 8, anisocyanate-reactive compound (3), said compound (3) having an averageequivalent weight of more than 374 and an average number ofisocyanate-reactive hydrogen atoms of from 2 to 6 and water in thepresence of a catalyst and in the presence of a fire retardant toprepare a rigid polyurethane foam and by crushing this rigidpolyurethane foam to prepare a flexible polyurethane foam.

Further the present invention is concerned with a polyisocyanatecomposition comprising the fire retardants.

More in particular the foams according to the present invention areprepared by reacting a polyisocyanate (1), a polyol (2) having ahydroxyl number of at least 150 mg KOH/g and an average nominal hydroxylfunctionality of from 2 to 8, a polyol (3) having a hydroxyl number offrom 10 to less than 150 mg KOH/g and an average nominal hydroxylfunctionality of from 2 to 6 and water in the presence of a catalyst anda fire retardant to prepare a rigid polyurethane foam and by crushingthis rigid polyurethane foam to prepare a flexible polyurethane foam.

Suitable organic polyisocyanates for use in the process of the presentinvention include any of those known in the art for the preparation ofrigid polyurethane foams, like aliphatic, cycloaliphatic, araliphaticand, preferably, aromaticpolyisocyanates, such as toluene diisocyanatein the form of its 2,4 and 2,6-isomers and mixtures thereof anddiphenylmethane diisocyanate in the form of its 2,4′-, 2,2′- and4,4′-isomers and mixtures thereof, the mixtures of diphenylmethanediisocyanates (MDI) and oligomers thereof having an isocyanatefunctionality greater than 2 known in the art as “crude” or polymericMDI (polymethylene polyphenylene polyisocyanates), the known variants ofMDI comprising urethane, allophanate, urea, biuret, carbodiimide,uretonimine and/or isocyanurate groups.

Mixtures of toluene diisocyanate and diphenylmethane diisocyanate and/orpolymethylene polyphenylene polyisocyanates may be used. Most preferablypolyisocyanates are used which have an average isocyanate functionalityof 2.1-3.0 and preferably of 2.2-2.8.

Preferably MDI, crude or polymeric MDI and/or liquid variants thereofare used said variants being obtained by introducing uretonimine and/orcarbodiimide groups into said polyisocyanates, such a carbodiimideand/or uretonimine modified polyisocyanate having an NCO value of atleast 20% by weight, and/or by reacting such a polyisocyanate with oneor more polyols having a hydroxyl functionality of 2-6 and a molecularweight of 62-500 so as to obtain a modified polyisocyanate having an NCOvalue of at least 20% by weight.

Isocyanate-reactive compounds (2) include any of those known in the artfor that purpose like polyamines, aminoalcohols and polyols. Ofparticular importance for the preparation of the rigid foams are polyolsand polyol mixtures having hydroxyl numbers of at least 150 mg KOH/g andan average nominal hydroxyl functionality of from 2 to 6. Suitablepolyols have been fully described in the prior art and include reactionproducts of alkylene oxides, for example ethylene oxide and/or propyleneoxide, with initiators containing from 2 to 8 active hydrogen atoms permolecule. Suitable initiators include: polyols, for example ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane, triethanolamine, pentaerythritol,sorbitol and sucrose; polyamines, for example ethylene diamine, tolylenediamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminated polythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Still further suitableisocyanate-reactive compounds include ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, butane diol, glycerol,trimethylolpropane, ethylene diamine, ethanolamine, diethanolamine,triethanolamine and the other initiators mentioned before. Mixtures ofsuch isocyanate-reactive compounds may be used as well. Most preferablypolyols are used which do not comprise primary, secondary or tertiarynitrogen atoms.

Isocyanate-reactive compounds (3) include any of those known in the artfor that purpose, like polyamines, aminoalcohols and polyols.

Of particular importance for the preparation of the rigid foams arepolyols and polyol mixtures having a hydroxyl value of 10 to less than150 and preferably of 15-60 mg KOH/g and an average nominal hydroxylfunctionality of from 2 to 6 and preferably of from 2 to 4. These highmolecular weight polyols are generally known in the art and includereaction products of alkylene oxides, for example ethylene oxide and/orpropylene oxide, with initiators containing from 2 to 6 active hydrogenatoms per molecule. Suitable initiators include: polyols, for exampleethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, butane diol, glycerol, trimethylolpropane, triethanolamine,pentaerythritol and sorbitol; polyamines, for example ethylene diamine,tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminatedpolythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Preferred polyols are thepolyether polyols comprising ethylene oxide and/or propylene oxide unitsand most preferably polyoxyethylene polyoxypropylene polyols having anoxyethylene content of at least 10% and preferably 10-85% by weight.Other polyols which may be used comprise dispersions or solutions ofaddition or condensation polymers in polyols of the types describedabove. Such modified polyols, often referred to as “polymer” polyolshave been fully described in the prior art and include products obtainedby the in situ polymerisation of one or more vinyl monomers, for examplestyrene and acrylonitrile, in polymeric polyols, for example polyetherpolyols, or by the in situ reaction between a polyisocyanate and anamino- or hydroxy-functional compound, such as triethanolamine, in apolymeric polyol.

The polymer modified polyols which are particularly interesting inaccordance with the invention are products obtained by in situpolymerisation of styrene and/or acrylonitrile in polyoxyethylenepolyoxypropylene polyols and products obtained by in situ reactionbetween a polyisocyanate and an amino or hydroxy-functional compound(such as triethanolamine) in a polyoxyethylene polyoxypropylene polyol.Polyoxyalkylene polyols containing from 5 to 50% of dispersed polymerare particularly useful. Particle sizes of the dispersed polymer of lessthan 50 microns are preferred. Mixtures of such isocyanate-reactivecompounds may be used as well. Most preferably polyols are used which donot comprise primary, secondary or tertiary nitrogen atoms.

The relative amount of isocyanate-reactive compound (2) and (3) orpolyol (2) and (3) may vary widely and preferably ranges from 0.1:1 to4:1 (w:w).

The relative quantities of the polyisocyanate and theisocyanate-reactive compounds to be reacted may vary within a widerange. In general an isocyanate index will be applied of from 25 to 300,preferably of from 30 to 200 and most preferably of from 102 to 150.

In order to prepare a foam water is used as a blowing agent. However ifthe amount of water is not sufficient to obtain the desired density ofthe foam any other known way to prepare polyurethane foams may beemployed additionally, like the use of reduced or variable pressure, theuse of a gas like air, N₂ and CO₂, the use of more conventional blowingagents like chlorofluorocarbons, hydrofluorocarbons, hydrocarbons andfluorocarbons, the use of other reactive blowing agents, i.e. agentswhich react with any of the ingredients in the reacting mixture and dueto this reaction liberate a gas which causes the mixture to foam and theuse of catalysts which enhance a reaction which leads to gas formationlike the use of carbodiimide-formation-enhancing catalysts such asphospholene oxides. Combinations of these ways to make foams may be usedas well. The amount of blowing agent may vary widely and primarilydepends on the desired density. Water may be used as liquid atbelow-ambient, ambient or elevated temperature and as steam.

A preferred combination of blowing agent is water and CO₂ wherein theCO₂ is added to the ingredients for making the foam in the mixing headof a device for making the foam, to one of the isocyanate-reactiveingredients and preferably to the polyisocyanate before thepolyisocyanate is brought into contact with the isocyanate-reactiveingredients.

Per 100 parts by weight of polyisocyanate (1), isocyanate-reactivecompound (2) and compound (3) or polyol (2) and polyol (3) and water,preferably the amount of compound (2) or polyol (2) ranges from 2-20parts by weight, the amount of compound (3) or polyol (3) ranges from5-35 parts by weight and the amount of water ranges from 1 to 17 partsby weight, the remainder being polyisocyanate. Most preferably theseamounts are 55-80, 3-20, 10-30 and 2-6 parts by weight for thepolyisocyanate, polyol (2), polyol (3) and water respectively. Thisencompasses another aspect of the invention: if a cyclic polyisocyanateand more in particular an aromatic polyisocyanate and most in particularan MDI or polymethylenepolyphenylene polyisocyanate is used the contentof cyclic and more in particular of aromatic residues in the flexiblefoam is relatively high as compared to conventional flexiblepolyurethane foams. The foams according to the invention preferably havea content of benzene rings, derived from aromatic polyisocyanates, whichis 30 to 56 and most preferably 35 to 50% by weight based on the weightof the foam. Since polyols, polymer polyols, fire retardants, chainextenders and/or fillers which contain benzene rings may be used, theoverall benzene ring content of the flexible foam may be higher andpreferably ranges from 30 to 70 and most preferably from 35 to 65%weight as measured by calibrated Fourier Transform Infra Red Analysis.

The present invention is more in particular concerned with a process forpreparing rigid polyurethane foams by reacting a polyisocyanate (1), apolyether polyol (2) having a hydroxyl number of at least 150 mg KOH/gand an average nominal hydroxyl functionality of from 2 to 8, apolyether polyol (3) having a hydroxyl number of from 10 to less than150 mg KOH/g and an average nominal hydroxyl functionality of from 2 to6 and water, wherein the amount of polyisocyante (1), polyol (2), polyol(3) and water is 55-80, 3-20, 10-30 and 2-6 parts by weight respectivelyper 100 parts by weight of polyisocyanate (1), polyol (2), polyol (3)and water, in the presence of a catalyst and a fire retardant andwherein the reaction is conducted at an isocyanate index of 70-150 andwherein the polyisocyanate is reacted with one or moreisocyanate-reactive compositions comprising one or more of theaforementioned polyol (2), polyol (3) and water (and not comprisingcompounds which have a primary, secondary or tertiary nitrogen atom,with the exception of a catalyst 2 and/or the protic acid of thiscatalyst 2, which catalyst 2 is discussed hereinafter and with theexception of part of the fire retardant which is also discussedhereinafter).

This preferred process gives foams with reduced thermal degradation,especially when such foams are made as large buns e.g. on a movingconveyor belt (slab-stock foam), the foams have improved stability and alow amount of extractables.

An even further preferred process is a process for preparing a rigidfoam by reacting a polyisocyanate (1), a polyether polyol (2) having anaverage equivalent weight of 70-300 and preferably of 70-150, having anaverage nominal hydroxyl functionality of from 2 to 6 and preferablyfrom 2 to 3 and an oxyethylene content of at least 75% by weight, apolyether polyol (3) having an average equivalent weight of 1000-3000,having an average nominal hydroxyl functionality of 2 to 3 andpreferably of 2 and having the structure

HO—(EO)_(X)—(PO)_(Z)—(EO)_(Y)—X[-0-(EO)_(Y)—(PO)_(Z)—(EO)_(X)H]_(n)  Formula1

wherein EO is an ethylene oxide radical, PO is a propylene oxideradical, x=1-15 and preferably 3-10, y=0-6 and preferably 1-4, z is suchso as to arrive at the above equivalent weight, n=1-2 and X is ahydrocarbon radical having 2-10 and preferably 2-6 carbon atoms or aradical having the formula —CH₂—CH₂—(OCH₂—CH₂)₁₋₂—, and water in thepresence of a catalyst and a fire retardant wherein the amount ofpolyisocyanate (1), polyol (2), polyol (3) and water is 55-80, 3-20,10-30 and 2-6 parts by weight respectively per 100 parts by weight ofpolyisocyanate (1), polyol (2), polyol (3) and water and wherein thereaction is conducted at an isocyanate index of 70-150 and wherein thepolyisocyanate is reacted with one or more isocyanate-reactivecompositions comprising one or more of the aforementioned polyol (2),polyol (3) and water (and not comprising compounds which have a primary,secondary or tertiary nitrogen atom, with the exception of catalyst 2,its protic acid and part of the fire retardant). Preferably the amountof water is 3-5 parts by weight calculated on the same basis as above.Preferably the weight ratio of water and polyol (3) is 0.1 to 0.4:1 andthe weight ratio of polyol (3) and of polyol (2)+water is 0.9-2.5:1

Most preferred polyether polyols (3) are those according to formula 1,described hereinbefore. Those having a nominal hydroxyl functionality of3 may be prepared by ethoxylation of an initiator, followed bypropoxylation and again ethoxylation, wherein the initiator is a triollike glycerol and/or trimethylol propane. Those having a nominalhydroxyl functionality of 2 may be prepared by ethoxylation of ethyleneglycol, diethylene glycol and/ortriethylene glycol, followed bypropoxylation and again ethoxylation; or by propoxylation of ethyleneglycol, diethylene glycol and/or triethylene glycol followed byethoxylation; or by propoxylation of a polyoxyethylene polyol having4-15 oxyethylene groups followed by ethoxylation. Mixtures of such mostpreferred polyols may be used as well. Although not necessary otherpolyols may be used together with these most preferred polyols accordingto formula 1, provided the amount does not exceed 30% by weight based onthe weight of these polyols according to formula 1. Such polyolsaccording to formula 1 are commercially available (e.g. Daltocel F 430from Huntsman Polyurethanes, Daltocel is a trademark of Huntsman ICIChemicals LLC).

As catalyst those may be used which enhance the formation of urethaneand urea bonds like amines, such as triethylene diamine, tin compounds,such as dibutyltin dilaurate and stannous octoate, and/or phosphateslike NaH₂PO₄ and Na₂HPO₄. Amine catalysts preferably are avoided, withthe exception of catalyst 2, see below. Preferably the followingcombination of catalysts is used: a tin salt of a carboxylic acid having2-18 carbon atoms (hereinafter called “catalyst 1”), together with alithium, sodium, potassium, rubidium, cesium, magnesium, calcium,strontium and/or barium salt of a protic acid, the acid having at least2 acidic hydrogen atoms and having a pK_(a) in water of 2-10(hereinafter called “catalyst 2”), in a ratio of catalyst 1: catalyst 2of 30:70 to 95:5 and in an amount of catalyst 1 and catalyst 2 of each0.1-5% by weight (calculated on the weight of all ingredients used toprepare the foam).

For simplicity reasons the above salts of the protic acids are called‘catalyst 2’; it is to be noted however that these compounds in facthave a deactivating effect upon catalyst 1. Without wishing to be boundby any theory it is believed that catalyst 2 supresses the formation ofcertain intermediate tin compounds during the preparation of the foam,which intermediate tin compounds would enhance certain undesirablehydrolytic processes which lead to said degradation.

The weight ratio of catalysts 1 and 2 as used in this process may rangepreferably from 50:50 to 90:10.

The carboxylic acid in catalyst 1 may be selected from saturated orunsatured aliphatic, cycloaliphatic and araliphatic hydrocarbons andfrom aromatic hydrocarbons having one carboxylic acid groups. Preferablythey have 2-18 carbon atoms. Most preferred monocarboxylic acids are thesaturated aliphatic carboxylic acids having 2-12 carbon atoms, likeacetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valericacid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid,decanoic acid, undecanoic acid and dodecanoic acid. Examples of tincatalysts of this type are dibutyltin dilaurate and stannous octoate.

The protic acid of catalyst 2 may be selected from a wide range ofcompounds.

Preferably such compounds are selected from those containing at least 2groups selected from —COOH and aromatic thiol.

Preferably the number of acidic hydrogen atoms is at least 3. Differentmetal salts may be used in combination. Further metal salts may be usedwherein all or only a part of the acidic hydrogens has been replaced bythemetal ion. Preferably 10-90% of the acidic hydrogen atoms has beenreplaced with the metal ion; when the acid is used instead of its saltmore tin catalyst is required in order to obtain the same gel time andwhen all acidic hydrogen atoms have been replaced with the metal ionscorching of the foam was observed when making bigger buns, e.g. from1800 g material. Most preferred salts are the K- and Na-salts.

Preferably catalyst 2 has a solubility in water of at least 5 gram ofcatalyst 2 per liter water at 25° C.

Examples of useful catalysts are the Li, Na, K, Rb, Cs, Mg, Ca, Srand/or Ba salts of: citric acid, 1,2,4,5 benzenetetracarboxylic acid(BCTA), ethylene-diaminetetraacetic acid (EDTA),ethylenebis-(oxyethylene-nitrilo)tetraacetic acid (EGTA).N-(2-hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA),1,3-diamino-2-hydroxypropane-N,N,N′,N′-tetraacetic acid (DHPTA),2-merca-ptobenzoic acid (MBA), 2,2′-thiodiglycolic acid (TDGA),poly(acrylic acid) (PAcA), poly(2-acrylamido-2-methyl-1-propanesulfonicacid) (PAcAmMPSA), copolymers of acrylamide and acrylic acid(PAcAm-co-PAcA), of acrylic acid and maleic acid (PAcA-co-PMA), ofvinylpyrrolidone and acrylic acid (PVP-co-PAcA), said polymers andcopolymers having average molecular weights between 500 and 1000000,preferably between 1000 and 500000.

The amount of catalyst 1 and catalyst 2 preferably varies from 0.2 to 3%by weight calculated on the weight of all ingredients used to preparethe polyurethane foam.

Catalysts 1 and 2 are preferably mixed with the isocyanate-reactivecompounds before the foaming reaction takes place. More preferablycatalyst 1 is mixed with a part of the isocyanate-reactive compounds andcatalyst 2 is mixed with another part of the isocyanate-reactivecompounds; subsequently these mixtures are fed to a mixing head of afoaming device where they are mixed with the polyisocyanate.

In addition to the polyisocyanate, the isocyanate-reactive compounds andthe blowing agent, one or more auxiliaries or additives known per se forthe production of polyurethane foams may be used. Such optionalauxiliaries or additives include foam-stabilizing agents or surfactants,for example siloxane-oxyalkylene copolymers and polyoxyethylenepolyoxypropylene block copolymers, anti-oxidants, anti-static agents, UVstabilisers, anti-microbial and anti-fungal compounds and fillers likelatex, TPU, silicates, barium and calcium sulphates, chalk, glass fibersor beads and polyurethane waste material. Preferbably additives andauxiliaries are used which do not comprise primary, secondary ortertiary nitrogen atoms.

In operating the process for making rigid foams according to theinvention, the known one-shot, prepolymer or semi-prepolymer techniquesmay be used together with conventional mixing methods and the rigid foammay be produced in the form of slabstock, mouldings including foam infabric and pour-in-place applications, sprayed foam, frothed foam orlaminates with other materials such as hardboard, plasterboard,plastics, paper or metal or with other foam layers.

It is convenient in many applications to provide the components forpolyurethane production in pre-blended formulations based on each of theprimary polyisocyanate and isocyanate-reactive components. Inparticular, an isocyanate-reactive composition may be used whichcontains the catalysts and the auxiliaries, additives and the blowingagent in addition to the isocyanate-reactive compounds (2) and (3) inthe form of a solution, an emulsion or dispersion.

The isocyanate-reactive components may also be supplied independently tothe polyisocyanate as two or more compositions containing the catalystsand the additives and auxiliaries; in particular one compositioncomprising catalyst 2 and/or the protic acid of catalyst 2, water andpolyol (2) and another composition comprising polyol (3), catalyst 1 andantioxidant may be fed from different storage tanks into the mixing headof a device for making foam, in which mixing head they are mixed withthe polyisocyanate. The relative amounts of catalyst 2 and/or the proticacid of catalyst 2, water and polyol 2 are 0.1-20, 10-55 and 35-85 partsby weight respectively and preferably 0.1-10, 10-55 and 35-85 parts byweight respectively per 100 parts by weight of catalyst 2 and/or theprotic acid of catalyst 2, water and polyol 2. Such compositions aremade by mixing the three ingredients.

As said before, catalyst 2 and/or the protic acid of catalyst 2preferably has a solubility in water of at least 5 gram of catalyst 2per liter water at 25° C. When catalyst 2 and/or the protic acid ofcatalyst 2 is used in the above composition it preferably has asolubility of at least 2 g of catalyst 2 and/or the protic acid ofcatalyst 2 per liter of polyol (2) and water irrespective of itssolubility in water alone.

Most preferably catalyst 2 is used in these compositions and processesfor making rigid polyurethane foams since it was found that the amountof tin catalyst, required to obtain a similar gel time, was higher whenthe protic acid of catalyst 2 was used.

The rigid foam is prepared by allowing the aforementioned ingredients toreact and foam until the foam does not rise any more.

After rise curing of the foam may be continued as long as desirable. Ingeneral a curing period of 1 minute to 24 hours and preferably of 5minutes to 12 hours will be sufficient. If desired curing may beconducted at elevated temperature. Subsequently the foam may be crushed.It is however preferred to allow the rigid foam obtained to cool down tobelow 80° C., preferably below 50° C. and most preferably to ambienttemperature prior to crushing. The rigid foam (i.e. before crushing)preferably has a core density of 3-35 and more preferably of 8-25 kg/m³(ISO 845).

The rigid foam (i.e. before crushing) prepared has a substantial amountof open cells. Preferably the cells of the rigid foam are predominantlyopen.

The crushing may be conducted in any known manner and by any knownmeans. The crushing may for instance be conducted by applying mechanicalforce onto the foam by means of a flat or pre-shaped surface or byapplying variations of external pressure.

In most cases a mechanical force sufficient to decrease the dimension ofthe foam in the direction of the crushing by 1-90%, preferably by 50-90%will be appropriate. If desired crushing may be repeated and/or carriedout in different directions of the foam. Due to the crushing the ballrebound increases considerably in the direction of the crushing. Due tothe crushing the density of the foam may increase. In most cases thisincrease will not exceed 30% of the density before crushing.

The foam may be crushed in the direction of foam rise. A special foam isobtained when the crushing is conducted in a direction perpendicular tothe direction of foam rise: then a foam is obtained with a highlyanisotropic cell structure.

Although it is difficult to give more precise directions for thecrushing since it will inter alia depend on the density of the foam, therigidity of the foam, the type of crushing device used, we believe thoseskilled in the art are sufficiently aware of the phenomenon of crushingof polyurethane foams that they will be able to determine theappropriate crushing manner and means with the above guidance, certainlyin the light of the following examples.

By crushing the ball rebound is increased at least in the direction ofcrushing. The increase is at least 10%. The core density of the flexiblefoam is 3-30 and preferably 3-20 kg/m³.

After the crushing the foam may be subjected to a heat treatment inorder to reduce the density increase caused by the crushing. This heattreatment is conducted at 70-200° C. and preferably at 90-180° C. for0.5 minute to 8 hours and preferably for 1 minute to 4 hours. After thecrushing and optionally the heating a novel flexible foam is obtainedwhich has exceptional properties.

Despite the fact that the foam is flexible, it does not show asignificant change of the Young's storage modulus E′ over a temperaturerange from −100° C. to +25° C., as described before. Further it shows aYoung's storage modulus at 25° C. of at most 500 kPa, preferably at most350 kPa, most preferably between 10-200 kPa and a sag factor (CLD 65/25,ISO 3386/1) of at least 2.0, preferably at least 3.5 and most preferablyof 4.5-10. CLD hysteresis loss values for the foams are below 55% andpreferably below 50% (which is calculated by the formula${\frac{\left( {A - B} \right)}{A} \times 100\quad \%},$

wherein A and B stand for the area under the stress/strain curve of theloading (A) and unloading (B) as measured according to ISO 3386/1).Still further these foams can be manufactured with a very low or evennegative Poisson's ratio as determined by lateral extension studiesunder compression of the foams. Finally compression set values of thefoams are generally low, preferably below 40% (ISO 1856 Method A, normalprocedure).

If the Tg^(h) is not too high the foam might be used in thermoformingprocesses to prepare shaped articles. Preferably the Tg^(h) of the foamis between 80 and 180° C., most preferably between 80° C. and 160° C.for such thermoforming applications. Further it was found that foams,which have been made by using a relatively low amount of the polyolshaving a low molecular weight, show a small or non-visible Tg^(h) byDMTA (the modulus change at Tg^(h) is small or the modulus changesgradually until the foam thermally decomposes); such foams may be usedfor thermoforming activities as well.

Further the foams show good load-bearing properties like compressionhardness values without the use of external fillers together with a goodresilience, tear strength and durability (fatigue resistance) even atvery low densities. In conventional flexible foams often high amounts offiller need to be used to obtain satisfactory load-bearing properties.Such high amounts of fillers hamper the processing due to a viscosityincrease.

The foams of the present invention may be used as cushioning material infurniture and automotive and aircraft seating and in mattresses, ascarpet backing, as hydrophilic foam in diapers, as packaging foam, asfoams for sound insulation in automotive applications and for vibrationisolation in general. The foam according to the present inventionfurther may be used together with other, conventional flexible foams toform composites, like e.g. in mouldings; such composites may also bemade by allowing the ingredients for making the conventional flexiblefoam to form said foam in a mould in the presence of the foam accordingto the present invention or alternatively by allowing the ingredientsfor making the rigid foam according to the present invention to formsaid rigid foam in a mould in the presence of the conventional flexiblefoam followed by crushing the moulding so obtained. Further the foamsaccording to the present invention may be used as textile cover, ascover for other type of sheets, as carpet underlay or felt-replacement;the so-called flame lamination technique may be applied to adhere thefoam to the textile, the carpet or the other sheet. In this respect itis important to note that the foam according to the present invention issuitable to be cut in sheets of limited thickness, e.g. of about 1 cmand less. Still further the foam according to the present invention maybe used as insulation material around pipes and containers.

The fire retardancy of foams which do not contain flame retardant is notsufficient to meet the test requirements for certain applications. Forexample, a foam which has not been combustion modified may typicallyhave an LOI of 18.4 and an MVSS302 burn rate of more than 150 mm/min. Itis therefore desirable, and in certain applications necessary, toincorporate fire retardants into the foam formulation in order toenhance the fire performance. For example, an LOI of more than 20 isoften desirable and an MVSS302 burn rate of less than 100 mm/min isnecessary for certain automotive applications.

The fire retardant used in the invention is a combination of 1)expandable graphite and 2) compounds of formula

wherein X, Y and Z are independently selected from the groups —R and—OR′ wherein R is an alkyl, aryl or aralkyl group having 1-12 andpreferably 1-10 carbon atoms, and R′ is an aryl or aralkyl group having6-12 and preferably 6-10 carbon atoms.

The expandable graphite is already known in the art.

The phosphorous-containing compounds include triphenylphosphine oxide,triphenylphosphate, triphenylphosphonate and compounds having one ormore, and preferably one, alkyl group(s) having 1-6 carbon atoms,attached to one or more of the aromatic rings of thesetriphenylphosphate, -phosphonate and -phosphine oxide, such as thecommercially available Reofos 50 and Kronitex CDP both obtainable fromFMC Corporation, which are isopropylated triphenyl phosphate andcresyldiphenyl phosphate, respectively.

Preferably, the relative amount of the compounds in such mixtures issuch that the weight ratio of phosphorous-containing compound toexpandable graphite is from about 1/9 to about 4/1.

The amount of fire retardants used to prepare the foam is preferablysuch that the combined weight of phosphorous-containing compound andexpandable graphite is 5-30%, most preferably 6-20%, by weightcalculated on the total formulation (polyisocyanate, polyols, water,catalyst, additives, auxiliaries and fire retardants).

The fire retardants may be fed to the mixing head of the device to makethe foam separately or after having been mixed. According to oneembodiment, the fire retardant system is premixed with theisocyanate-reactive composition or with the isocyanate composition. Suchcompositions also are part of the present invention. The amount of fireretardant(s) in the polyisocyanate composition is 5-40% by weight andpreferably 8-30% by weight whereas the amount of fire retardant(s) inthe isocyanate-reactive composition is 20-75% by weight, preferably25-60% by weight calculated on the amount of composition and fireretardant. Preferably, the fire retardants are pre-mixed with theisocyanate-reactive composition.

Such compositions are prepared by combining the ingredients in any orderunder ambient conditions or, if desirable, at elevated temperaturefollowed by normal or high shear mixing. Experiments have shown that theprocess conditions for preparing the rigid foams are relativelydemanding. The fire retardants used in the present invention provide forreduced levels of or the avoidance of scorching; they showed to besufficiently stable; they can be provided as liquids or as liquiddispersions which makes them easily processable in making the foams andthey provide good fire retarding properties to the foams made.

Further the fire retardants mentioned before may be used together withother fire retardants and in particular together with melamine and/orguanidine carbonate. The amount of such other fire retardant is 0.5-20%by weight and preferably 1-10% by weight calculated on the totalformulation.

Mixtures of fire-retardant systems of the invention and/or mixtures ofexpandable graphite and/or mixture of phosphorous-containing compoundare also contemplated.

The use of the phosphorous-containing compound allows the reduction ofthe viscosity of a composition (either polyol or polyisocyanate)containing the expandable graphite. This composition having a lowerviscosity (such as below 10 Pa.s, preferably below 1 Pa.s) allows animproved processability. Preferably, the phosphorous-containing compoundallows the reduction of the viscosity of the polyol compositioncontaining the expandable graphite.

The above fire-retardant system is halogen-free and thus avoids anyproblem traditionally associated with halogens, which problems arenowadays to be eliminated.

The invention is illustrated by the following examples.

EXAMPLES 1-11

A catalyst containing polyol blend, blend A, was prepared by mixing 22pbw of ‘DABCO’ T9 (catalyst from AIR PRODUCTS, DABCO is a trade mark),350 pbw of an EO/PO polyol having a nominal functionality of 2,diethylene glycol as initiator, an EO content of 20.2% by weight (alltipped) and an hydroxyl value of 30 mg KOH/g.

A water containing blend, blend B, was prepared by dissolving 36 pbwEDTA-3Na in 400 pbw water. Subsequently 755 pbw of polyethylene glycolhaving a molecular weight of 200 and 235 pbw of triethylene glycol wereadded to this solution under continuous stirring.

A stabiliser containing polyol blend, blend C, was prepared by mixing 28pbw of ‘IRGANOX’ 1135, 1.1 pbw of ‘IRGAFOS’ TNPP (stabilisers fromCiba-Geigy, IRGANOX and IRGAFOS are trade marks), 500 pbw of an EO/POpolyol having a nominal functionality of 2, diethylene glycol asinitiator, an EO content of 20.2% by weight (all tipped) and an hydroxylvalue of 30 mg KOH/g.

A polyisocyanate mixture, blend D, was prepared by mixing 184.4 pbw ofpolymeric MDI having an NCO value of 30.7% by weight and an isocyanatefunctionality of 2.7 and 159.6 pbw of a uretonimine modified MDI havingan NCO value of 31% by weight, an isocyanate functionality of 2.09, auretonimine content of 17% by weight and 2,4′- MDI content of 20% byweight.

All the fire retardants, with the exception of the expandable graphite,were either mixed with the isocyanate mixture or mixed with one of thepolyol streams prior to making a foam, or were added as a separatestream. The expandable graphite was added as a separate stream or withthe polyol stream. The expandable graphite and phosphorous-containingcompound are introduced together with the polyol in examples 10 and 11.

Adding expandable graphite to the polyol increases the viscosity of thepolyol stream. When the expandable graphite level for example 9 wasadded to half of the required EO/PO polyol, the viscosity of the mixturewas measured to be around 50 Pa.s (at 30° C.). If the same expandablegraphite level is added to all of the required EO/PO polyol, then theviscosity of the mixture was measured to be around 5 Pa.s.

If the expandable graphite and the phosphorous-containing compounds arecombined and added to all of the required EO/PO polyol as in example 10,then the viscosity of the mixture was measured to be below around 1Pa.s.

In the table below the actual weight amount of chemicals used to producethe foam are given. All foams were produced at an isocyanate index of100, with the exception of examples 9, 10 and 11, which were produced atan isocyanate index of 104. The reactant streams are first added to avessel for mixing and are then transferred to a mould. The mixing vesselis typically a 750 ml paper cup, but a 51 bucket was used in examples 9,10 and 11. The mould used was typically a 51 bucket, but a 0.5×0.5×0.25m open box was used in examples 9, 10 and 11. First blend B is broughtinto the mixing vessel. Subsequently blends C, A and D are added. Thecontent of the cup is mixed for 13 seconds with a ‘HEIDOLPH’ mechanicalmixer (HEIDOLPH is a trade mark) at a speed of 5000 rpm. After mixingthe reaction mixture was poured into the mould and allowed to react. Thegel time amounted to 40 to 50 seconds and the rise time amounted to 70to 90 seconds. After at least 15 minutes the foam was taken out of thebucket and allowed to cool to ambient temperature. A rigid polyurethanefoam was obtained. Prior to fire testing the foam samples were crushedby one compression (70% CLD) at 100 mm/min in the rise direction,followed by 10 crushings (70% CLD of the height after the firstcompression) at a rate of 500 mm/min in the rise direction of the foamusing an INSTRON (INSTRON is a trade mark) mechanical tester mountedwith flat plates. After crushing a flexible foam was obtained which hadno major glass-rubber transitions between −100° C. and +25° C.

The foams were submitted to the US Safety Standard FMVSS 302 rate offlame spread test for motor vehicle interior components and the limitingoxygen test according to ASTM D2863/91.

The following fire retardants were tested and compared:

DE-71 from Great Lakes is pentabromodiphenyl oxide containing 71 wt % Br

Reofos 50 from FMC Corp. is isopropylated triaryl phosphate containing8.4 wt % P

Callotek grades from Graphitwerk Kropfmuehlm AG are expandable graphite.

The LOI and MVSS burn rate test results for example 1 to 11 are given inthe table below:

TABLE Example 1 2 3 4 5 6 7 8 9 10 11 Blend A 21.26 21.26 21.26 21.2621.26 21.26 21.26 21.26 155.22 155.22 155.22 Blend B 28.52 28.52 28.5228.52 28.52 28.52 28.52 28.52 208.22 208.22 208.22 Blend C 21.16 21.1621.16 21.16 21.16 21.16 21.16 21.16 154.5 154.5 154.5 Blend D 153.4153.4 153.4 153.4 153.4 153.4 153.4 153.4 1.165 1.165 1.165 Callotek 1000 14.32 22.2 30.6 0 0 14.32 6.94 0 104.6 0 Callotek 200 0 0 0 0 22.2 0 00 162.1 0 104.6 Callotek 600 0 0 0 0 0 22.2 0 0 0 0 0 Reofos 50 7.3 0 00 0 0 7.88 23.66 0 57.53 57.53 DE71 14.7 0 0 0 0 0 0 0 0 0 0 Cream time(s) 20 17 18 17 16 22 20 25 18 15 15 String time (s) nd 39 36 44 39 5046 55 65 43 53 wt % Callotek 0 6 9 12 9 9 5.8 2.7 8.9 5.7 5.7 wt %Reofos 50 3 0 0 0 0 0 3.2 9.3 0 3.1 3.1 wt % DE-71 6 0 0 0 0 0 0 0 0 0 0wt % P 0.25 0 0 0 0 0 0.26 0.77 0 0.26 0.26 wt % Br 4.25 0 0 0 0 0 0 0 00 0 LOI (%) 21.2 20.6 22.6 22.7 22.0 22.2 22.2 22.2 21.8 21.4 22.0MVSS302 (mm/min) 47 97.4 nd nd nd nd nd nd nd 45 44 nd: not determined

What is claimed is:
 1. Process for preparing a rigid foam by reacting apolyisocyanate (1), an isocyanate-reactive compound (2), said compound(2) having an average equivalent weight of at most 374 and an averagenumber of isocyanate-reactive hydrogen atoms of from 2 to 8, anisocyanate-reactive compound (3), said compound (3) having an averageequivalent weight of more than 374 and an average number ofisocyanate-reactive hydrogen atoms of from 2 to 6 and water in thepresence of a catalyst and in the presence of a fire retardant whereinthe fire retardant is a combination of 1) expandable graphite and 2)phosphorous-containing compounds of formula:

wherein X, Y and Z are independently selected from the groups —R and—OR′ wherein R is an alkyl, aryl or aralkyl group having 1-12 andpreferably 1-10 carbon atoms, and R′ is an aryl or aralkyl group having6-12 and preferably 6-10 carbon atoms and wherein thephosphorous-containing compounds are selected from triphenylphosphineoxide, triphenylphosphate, triphenylphosphonate and compounds having oneor more, and preferably one, alkyl group(s) having 1-6 carbon atoms,attached to one or more of the aromatic rings of thesetriphenylphosphate, -phosphonate and -phosphine oxide.
 2. The processaccording to claim 1, wherein the weight ratio of phosphorous-containingcompounds to expandable graphite is from about 1/9 to about 4/1.
 3. Theprocess according to claim 1, wherein the combined weight ofphosphorous-containing compounds and expandable graphite is 5-30%, mostpreferably 6-20%, by weight calculated on the total formulation. 4.Process for preparing a flexible foam by crushing the rigid foamprepared according to the process according to claim
 1. 5.Isocyanate-reactive composition comprising an isocyanate-reactivecompound (2), said compound (2) having an average equivalent weight ofat most 374 and an average number of isocyanate-reactive hydrogen atomsof from 2 to 8, and an isocyanate-reactive compound (3), said compound(3) having an average equivalent weight of more than 374 and an averagenumber of isocyanate-reactive hydrogen atoms of from 2 to 6, and a fireretardant wherein the fire retardant is a combination of 1) expandablegraphite and 2)) phosphorous-containing compounds of formula:

wherein X, Y and Z are independently selected from the groups —R and—OR′ wherein R is an alkyl, aryl or aralkyl group having 1-12 andpreferably 1-10 carbon atoms, and R′ is an aryl or aralkyl group having6-12 and preferably 6-10 carbon atoms and wherein thephosphorous-containing compounds are selected from triphenylphosphineoxide, triphenylphosphate, triphenylphosphonate and compounds having oneor more, and preferably one, alkyl group(s) having 1-6 carbon atoms,attached to one or more of the aromatic rings of thesetriphenylphosphate, -phosphonate and -phosphine oxide.